The developer solution for developing color photographic materials, in particular for developing color photographic paper, is prepared from or, in the case of continuous operation, replenished with concentrates which contain the necessary constituents.
It is conventional to provide three different concentrates, as certain constituents of the developer bath are not mutually compatible on extended storage. Thus, for example, one concentrate contains the antioxidant, an auxiliary solvent and an optical brightener, a second concentrate contains the color developer substance, for example CD 3 (N-ethyl-N-(2-methylsulfonylaminoethyl)-3-methyl-p-phenylenediamine) and a third concentrate contains the buffer substance, alkali and a water softener.
The first concentrate is alkaline (approx. pH 10), the second is strongly acidic and thus stable with regard to color developer concentration and the third is strongly alkaline. A small quantity of sulfite is generally added to the concentrate of the color developer substance for stabilisation purposes. The quantity of sulfite must not be too large as it otherwise has a negative impact on sensitometry (inhibition of development and thus reduction of color densities).
There has been no lack of attempts to develop stable, one-part color developer concentrates as handling errors during preparation or replenishing of a developer solution may consequently be avoided.
Two one-part concentrates are currently commercially available, a) Monoline(copyright) RA-4 CD-R from Tetenal, a two-phase concentrate with a solid, undissolved phase deposited at the bottom and b) TriPhase(copyright) RA-4 CD-R from Trebla, a three-phase concentrate with undissolved constituents in the middle phase (c.f. also U.S. Pat. No. 5,891,609).
In both cases, the presence of undissolved constituents is disadvantageous for the purposes of handling the concentrate. Especially when preparing the regenerating solution, problems may occur because the undissolved constituents dissolve only poorly.
A two-part concentrate of a color developer is known from U.S. Pat. No. 4,232,113. The part containing the developer substance which is a p-phenylenediamine compound contains only organic solvents and has to be substantially free of water. This is disadvantageous on an economical as well as on an ecological view.
The object of the invention was to provide a two-part concentrate for a color developer, neither part of which contains any undissolved constituents, from which parts a regenerating solution may rapidly be produced, which parts comprise a single phase and which avoid larger amounts of organic solvents.
This object is achieved by part 1 of the two-part concentrate containing diethylhydroxylamine or diethylhydroxylamine disulfo acid as the antioxidant containing the auxiliary solvent, the optical brightener, the color developer substance, 0.001 to 1 mol of hydroxylamine or a monoalkylated hydroxylamine or the salts thereof per liter of concentrate and at least 20% by weight, preferably at least 30% by weight of water based on the total of part 1.
Preferably, 0.005 to 0.3 mol of hydroxylamine or monoalkylated hydroxylamine or the salts thereof are used, particularly preferably hydroxylammonium sulfate.
Part 1 preferably has a pH of 1.5 to 6.
Part 2 of the two-part concentrate corresponds to the previous part 3, comprising the buffer substance, alkali and water softener.
Monoalkylated hydroxylamine is preferably of the formula
HOxe2x80x94NHxe2x80x94R
in which
R means C1-C10-alkyl, hydroxy-C1-C10-alkyl, C1-C10-alkoxy-C1-C10-alkyl carboxy-C2-C10-alkyl, dicarboxy-C1-C10-alkyl, carboxyhydroxy-C1-C10-alkyl, hydroxy-C1-C5-alkyl-(oxy-C1-C5-alkyl)n, C1-C5-alkoxy-C1-C5-alkyl(oxy-C1-C5-alkyl)n or aryl and
n means a number from 1 to 4.